MACROCYTOSIS is present in any condition in which there is an outpouring of immature red blood cells or in which there may be faulty absorption, utilization, or storage of the erythrocyte-maturing factor (E.M.F.). It may be suspected on routine examination of the stained blood smear, but an accurate diagnosis must await the actual measurement of the mean cell diameter by means of an erythrocytometer or the calculation of the volume index. The volume index is determined by dividing the per cent normal red blood count into the per cent normal hematocrit reading. A volume index of 1.08 or above indicates macrocytosis.

With any sudden demand upon the hematopoietic system precipitated by an acute loss of blood, the bone marrow endeavors to compensate by releasing immature red blood cells, or reticulocytes, which are larger than mature erythrocytes. This results in reticulocytosis, which may at times reach levels as high as 45 or 50 per cent.

An example of this condition was found in a 24-year-old girl with portal hypertension. During the preceding ten years she had had repeated episodes of hematemesis, for which 81 transfusions had been given. Two years after the onset of bleeding a splenectomy had been performed at another institution, and this was followed by multiple injections of esophageal varices. During the course of several hospitalizations a devascularization of the stomach and several esophagoscopies were carried out in an effort to control bleeding points. She had recently been hospitalized for a recurrence of severe hematemesis, at which time. . .